Process of forming powdered metal parts in atmosphere containing hbr and articles resulting therefrom



- Oct. 9, 1956 TENS/L E S TEE/V6 H. L. CROWLEY ETAL 2,765,519 PROCESS OFFORMING POWDEIRED METAL PARTS IN ATMOSPHERE CONTAINING HBY AND ARTICLESRESULTING THEREFROM Filed March 7, 1952 f 20,000 z 000 i MMF 15000 1000014,000 14,000 10,000 $10,000 L X V) 11000 11,000 4 [u .1- Q 10,000 P10,000

.0 b 0,000 R 0,000 L\ TEMPERATURE "F H Br PRE E IN VEN TOR-S I 2 g: gHeqrg L. flan/leg g 0 2 a I a 7 HB. /Varmn E'rnesifimfiano O 5. 0 0 r ag. 2, 3 W3 (QMM 1 United States Patent 2,765,519 Patented Oct. 9, 1956PROCESS OF FORMING POWDERED METAL PARTS IN ATMOSPHERE CONTAKNING HBr ANDARTICLES RESULTING THEREFROM Henry L. Crowley, South Orange, N. J., andMarion Ernest Graham, Par-ma, Ohio, assignors, by direct and mesneassignments, to Republic Steel Corporation, Cleveland, Ohio, acorporation of New Jersey Application March 7, 1952, Serial No. 275,38217 Claims. (Cl. 29-1825) The present invention relates to a process ofheat treating powdered metal parts and more particularly to heattreating and/or sintering such parts formed by pressing powdered metalinto a desired shape in order that the parts, as heat treated orsintered, shall have the desired physical characteristics. The presentinvention also relates to parts such as those which are formed by thepresent process.

The present application is related by similarity of subject matter toour prior and copen-ding application, Serial No. 166,312, filed June 6,1950, now abandoned and entitled Process of Heat Treating Powdered MetalParts and Parts Formed Thereby. Said application Serial No. 166,312 wasfollowed by a continuation-in-part thereof, Serial No. 300,908, filedJuly 25, 1952, which had the same title as Serial No. 166,312. Thisapplication is now abandoned but has been replaced by a furtherapplication Serial No. 575,794, which was copending with Serial No.300,908 and is a continuation-impart thereof. Serial No. 575,794 has thetitle Process of Heat Treating Powdered Metal Parts. The line ofdemarcation between these two inventions is based on the principle thatwhen the atmosphere in which the parts are sintered contains HCl, thesubject matter is included in said application, Ser. No. 575,794; whilethe present case is restricted to those situations wherein the sinteringatmosphere con- 1 tains HBr.

In the past, it has been customary in the making of parts by so-calledpowder metallurgy practices to select the powder of one or more metals,mix if powders of more than one metal are used, compact this powder in asuitable mold under relatively high pressure, then sinter the pressedparts in a non-oxidizing atmosphere at a suitable temperature, which ischosen in respect to the composition of the parts, in order that themetal powder shall be bound together into the desired article. Parts soformed are usually not as strong as a part made from cast metal ofsubstantially the same chemical composition respectively, but they havethe advantage that little or no machining need be done following theformation of the desired part in this way. As a result, the parts may begiven adequate mechanical strength for some particular purposes, notrequiring the strength of cast metal parts, and at the same time be mademuch quicker and cheaper. Such prior art processes have been appliedusing single metals and using combinations of metals, usually by mixingthe powders of two or more metals in desired proportions. Theatmospheres in which the heat treating or sintering has been done areuniformly non-oxidizing in character, but within that limitation, havebeen of many different types. All this prior art practice is now quitewell known and is described in numerous text books on the subject.

The present invention improves this prior art practice in a substantialmanner in that parts may be formed and heat treated in accordance withthe present invention, so as to have greatly enhanced physicalproperties, for ex ample, tensile strength and elongation, when heattreated at the same temperatures that would have been used in accordancewith prior art practices. Alternatively, at least as good physicalproperties may be imparted to a given part as in the prior art, whileusing substantially lower temperatures for the heat treating than wasthought possible in accordance with prior art practices. intermediateresults may be obtained in accordance with the present invention,including somewhat enhanced physical properties as aforesaid, whileusing somewhat lower temperatures than were considered standard inaccordance with the prior art teachings.

Summarizing the present invention, the processes in accordance therewithall involve heat treating inan atmosphere containing at least about 1%HBr by volume. Although it has been found that the addition of amountsof HBr, less than about 1% by volume to the sintering atmosphere, are oflittle, if any, advantage and in some cases are even deleterious to thephysical properties of the part sintered therein; at concentrations ofat least about 1% HBr and above in the atmosphere, the improvements inphysical properties of the parts made according to the present processare more or less proportionate to the concentration of HBr in theatmosphere about the parts during the heat treatment up to about 5% HBrconcentration in this atmosphere by volume. The enhanced characteristicsof the final product have been found to reach their peaks at about 5% toabout 15% by volume of gaseous HBr in the atmosphere, so that it ispointless to use any higher percentage and, in fact, from some points ofview, as hereinafter set forth, the use of higher concentrations of H131may be undesirable.

Metals which are susceptible of being formed into parts, in accordancewith the present invention, are

' broadly, relatively diflicultly bromidizable metals, namely,

tion will be brought out more specifically hereinafter and will beillustrated by actual examples of the present process.

The present invention also includesthe products made in accordance withthe present process, which are characterized by (substantially greatertensile strength than similar articles made by the identical process,with the exception that the sintering atmosphere contains less thanabout 1% by volume of HBr or is substantially free of HBr. 'Such novelproducts of the present process are usually also characterized bysubstantially greater elongations under tension in respect to similararticles.

Considering now details of the present invention and the principlesgoverning it, there will be discussed first the metal or metals whichmay be used in accordance with this invention. Broadly, as aforesaid,the metals usable are practically restrictedto those metals which arerelatively difficult to bromidize. The list of such appropriate metalsis given above. This list includes all the metals now known who usable,singly or in combination, in metal parts whichmay be processed inaccordance with the present invention. In the event that some one of therelatively easily bromidizable metals, such as zinc, aluminum ormagnesium, be present in any substantial amount, either alone, as aningredient of a mixture, or as one metal forming an alloy with someother metal or metals which may be in the acceptable list given above,trouble is encountered. For-example, brass, an alloy consisting ofcopper and zinc, is not susceptible of use when such alloy powder isused in forming the parts to be made, for the reason that the zinctendst'o bromidi'ze easily and defeats the purpose to be attained by thepresent invention as aforesaid. In contrast to this, bronze powders,consisting of copper and tin, both in the acceptable group, may beformed and heat treated in accordance with the present invention as willappear more particularly from the examples hereinafter given. t

The present invention is applicable when one or more metals are used,whether the metals, if two or more-,be introduced as separate powders ofthe individual metals or as alloy powders, i. e., wherein eachparticleof the powder is an alloy. When ual metals are originally used in makingthe parts, there is considerable evidence that there is increasedinterdiffusion of the metal particles when operating in accordance withthe process of the present invention as compared with prior artprocesses.

The theory, which is now believed to he basically correct, but is notparticularly relied upon in support of the patentability of the appendedclaims, is that when relatively large amounts of HBr are present in theatmosphere during heat treating, relatively easily bromidizable metalsare attacked by the HBr to such an extent that the final product haspresent therein substantial amounts of the bromides of the easilybromidizable metals and/or is porous due to the volatilization of suchbromides, leaving spaces formerly occupied by the bromidized metals. Ineither event, there results a product, difierent in composition from themetal powder which was subjected to the pressing operation andintroduced into the heat treating step, which product has, in fact, lessdesirable physical characteristics than would be present if prior artpractices were employed using a non-oxidizing atmosphere without HBrpresent therein. The process may, therefore, be said to be applicable tothe metals-iron, nickel, cobalt, copper, lead, cadmium, tin andmolybdenum or to mixtures or alloys thereof, as far as is now known.

The next major factor to be considered in the present case is theatmosphere which is to be used during the heat treating. This atmospheremust be essentially non-oxidizing in character. It may be neutral orreducing, but cannot be, to any substantial extent, oxidizing. Many suchatmospheres (absent HBr) have been tried in the prior art, so that noparticular details need be given hereof the large number of differentpossible non-oxidizing atmospheres which are usable. It is found thatnitrogen, at neutral gas, is operative as the non-oxidizing atmosphere.It has been found, however, that when the atmosphere surrounding theparts during the heat treatment used is reducing in character, such asgas containing a substantial amount of or consisting entirely ofhydrogen (other than the HBr present therein), better results areobtained than with a strictly neutral gas. Thus, the preferredatmosphere, in accordance with the present invention, is one in whichthere is a substantial proportion of hydro gen. The theories nowavailable tending to explain this will be set forth hereinafter.

The essential distinction between the present invention and the priorart is in the use of some gaseous HBr (at least about 1% by volume) as apart of the atmosphere surrounding the metallic parts during the heattreatment thereof. It is found that when this process is carried on, theparts as finally made and as a result of the heat treatment, haveenhanced physical characteristics of tensile strength and elongation, inrespect to articles made in the same way throughout, with the exceptionthat the atmosphere in which they are heat treated contained no HBr oramounts thereof of less than about 1% by volume. These differences willbe apparent from particular examples hereinafter given and from theaccompanying drawings.

The advantages to be gained by the presence of HBr in the gassurrounding the articles in the heat treatment is more or lessproportionate to the concentration of separate powders of individvolume)are reached. In this range of concentrations, a

plot of the value of certain physical characteristics against HBrconcentration levels off. Based upon plots of this kind, such as areshown in the accompanying drawings, it is the principle of thisinvention that any amount of HBr above about 1% by volume isadvantageous. Preferred ranges, however, of concentration of HBr, inaccordance with the present invention are from about 1% to about 15% byvolume. For maximum advantages from the point of view of physicalcharacteristics of the final product, in accordance with the presentinvention,

the range of about 5% to about 15% is found to be preferred, Beyond 15%there seems to be no purpose in increasing HBr concentration, as thecost of the operation is increased to some extent and the physicalproperties of the final product, not substantially better. In additionto this, as the concentration of HBr in the gas is raised, the tendencytoward bromidizing some of the metal present is correspondinglyincreased.

This point is related to the theories now believed to be correct for theuse of atmospheres containing some reducing gas as hydrogen. Takingiron, for example, there is a progressively increasing tendenc as theHBr concentration is increased, for a reaction to occur between iron andthe HBr to form ferrous bromide. If any ferrous bromide be formed, eveninstantaneously, any hydrogen present in the gas will tend to reduce itto reform iron and to liberate HBr in gaseous form. Thus, from anoverall point of view, the presence of hydrogen in the atmosphere tendsto prevent the formation and possible subsequent volatilization offerrous bromide. Corresponding reactions can occur between other metalspresent and HBr. .For this reason, it is usually preferred to keep aslow an HBr concentration as possible consistent with obtaining desiredresults, provided, of course, that the concentration of HBr be kept atat least 1% by volume, while at the same time having present in the gassome hydrogen. Another factor to be considered is the tendency for gascontaining HBr to corrode apparatus in which the process is carried on.Here again, in orderto minimize such corrosion,it is usually desirableto use as low a concentration of HBr as can be used (provided it is atleast 1% by .volume),.while still obtaining the advantages of thepresent invention in producing articles having enhanced physicalproperties.

In contrast with the above, it is the present theory that when HBr isused in accordance with the present invention in an atmosphereconsisting, apart from HBr, of a neutral gas such as nitrogen, thereare. opposing effects. The presence of HBr will give enhanced physicalcharacteristics in the final product, in accordance with the present.invention. On the other hand, the presence of HBr in the absence of astrongly reducing gas, such as hydrogen, will result in some bromidizingof the metal. This, in turn, willresult in relatively less desirablephysical properties. The net result is believed to be a balance. betweenthese two effects. i

Several theories have been expressed tending to explain the novel andhighly beneficial results obtained from the practice of the presentinvention. One of these theories is that the HBr present acts in amanner similar to a pickling bath in that it serves to clean thesurfaceof the metallic particles by removing any oxide film therefrom.

This leaves the particles with clean surfaces, which are enabled moreefficiently to sinter together, so as to form a superior article under agiven set of conditions. The removal of the oxides thus results inenhanced physical characteristics in the final article.

Concentrations of H31 substantially less than Another theory, which hasbeen expressed and which perhaps partakes of the first expressed theoryto some extent, is that the HBr present in the gas reacts with any metaloxides present to convert them to the respective bromides. Thesebromides, in a process employing a gas containing some hydrogen, may bereduced; and the reduced metal so formed may then act as a cement orhinder to bind the particles of the original material together. In suchan event, the HBr acts in effect as a catalyst, as it is regenerated bythe reduction reaction with hydrogen.

Although the process of the present invention, namely, sintering in anatmosphere containing at least 1% HBr by volume, has been found to besimilar in some respects to our copending application, Serial No.166,312 aforesaid, it is to be noted that while in our formerapplication it was found that the enhancement of certain physicalproperties, such as tensile strength, has been found more or lessproportional to HCl present in the sintering atmosphere up to about 15%,this is not the case when the sintering is carried out in an atmospherecontaining HBr according to the present invention. It has further beenfound and will be particularly illustrated by specific examples, thatthe presence of small amounts of HBr in the sintering atmosphere,namely, amounts substantially less than about 1% by volume, not onlyfail to enhance the physical properties of the parts being treated, butactually have a substantial adverse eifect on those properties. Atconcentrations of about 1% or more by volume of HBr and up to about 5%,it is found that the enhancement of physical properties is substantiallyproportional to the concentration of HBr. No explanation is known at thepresent time for the apparently anomalous behaviour of HBr when presentin concentrations of substantially below 1% by volume. Thus, in thepresent invention, the lower limit of HBr concentration is somewhatcritical as will be illustrated by subsequent examples.

While the theories herein are now believed to be correct, theatentability of the appended claims is not predicated upon thecorrectness of these theories; but rather upon thenovel combination ofprocess steps and the novel product specifically recited herein. It isnot known exactly why these improved results occur. It is known,however, that they do in fact occur and that they are reproducible whenthe teachings of this application are followed. It appears that the HBrmust be present in gaseous form in the atmosphere surrounding thearticles. This was proven by the fact that While gaseous HBr waselfective in securing enhanced physical properties in an iron body orarticle, no desirable results were attained when using a reducingatmosphere as in the prior art and when bromide Was supplied in the formof solid ferrous bromide intermixed with iron powder as a part of thearticle to be heat treated. This Was so even when the atmosphere usedsurrounding the ferrous bromide containing article consisted solely ofhydrogen. This result was surprising in view of the fact that it isknown that in an atmosphere of hydrogen, ferrous bromide may be reducedto metallic iron at the temperature at which this article was held forheat treatment. Under the circumstances of the test, wherein thepowdered iron article contained solid FeBrz, the article produced had alower strength as compared with an article formed of powdered iron andheat treated in accordance with the priorart at the same temperature.From this, it was concluded that in order to attain the desired resultsof the present process, it is not feasible to supply a bromide, as solidferrous bromide, admixed in the article itself, so that HBr must beotherwise su plied to, or be present in, the gases. surrounding thearticle during heat treatment.

It has further been found that while a bromide, such as FeBrz,intermixed with the metallic material being sintered, exerts anundesired influence upon the tensile strength of the resulting sinteredarticle, the presence of gaseous HBr in the sintering atmosphere alwaysexerts a beneficial influence, even when some bromide is present in anintermixed condition. Intermixed bromide cannot properly be relied uponto provide HBr in the gases even whena reducing gas, such as hydrogen,is present; but such HBr must be provided from a separate source. Thusthe amount of bromides intermixed in the metallic material should beminimized in order to minimize the deleterious effect thereof on thetensile strength of the articles being made. At the same time theundesired effects of the presence of small amounts of bromide in themetallic material being sintered (such as might be present as animpurity) may be compensated for by providing an ample amount of HBr inthe sintering atmos phere which is supplied from a source independent ofintermixed bromide or bromine-containing material.

The next and last major factor to be considered in the present processis the temperature at which the heat treating takes place. In accordancewith the prior art wherein the gaseous atmosphere did not contain HBr,such temperatures were in fact standard, or substantially so, for anygiven metal or combination of metals. For example, with the powderediron, the temperature used was about 2000 F. This standard temperature,chosen in accordance with the'prior art, may be defined as that at whichat least one metal present is brought to the point of incipient fusion.At the same time, these standard temperatures were always less than themelting point of the highest melting metal present. As such, therefore,the temperatures varied substantially depending upon the composition ofthe metal or metals contained in the part being heat treated. For thepurpose of the present discussion, these prior art sinteringtemperatures in an atmosphere in which HBr was absent may be termedstandard temperatures. Such standard temperatures may be found in manytextbooks and articles treating this subject matter.

In accordance with the present invention, the process may be practicedat the standard temperature as aforesaid for the material in questionand thereby greatly enhanced physical characteristics obtained in thefinal article, particularly tensile strength, and elongation. Thispractice represents one embodiment of the present invention.

Another embodiment of the present invention from this point of view isthe corresponding operation at substantially reduced temperatures inrespect to standard temperatures as aforesaid respectively. At suchreduced temperatures, which are substantially less than the standardtemperatures for any given metal composition respectively, at least asgreat or as desirable physical properties may be attained in the finalproduct as would result from the practice of prior art processes withrespect to the same type article. For example, taking the case of aniron article, the standard temperature of the prior art is about 2000 F.when using an atmosphere containing no HBr. In accordance with thepresent invention, a final article formed from iron powder can beprepared using a sintering temperature of about 1600 F. and having atleast as desirable physical properties of strength and elongation. Thus,in accordance with this embodiment of the process of the invention,substantially less heat is required, with a corresponding saving in thecost of the heat and in Wear and tear on the equipment used incident tothe use of higher temperatures.

Intermediate practicesmay also be used in accordance with the presentinvention using temperatures between the standard temperature and thelowest temperature possible as aforesaid, which may be expressed assomewhat lower than the standard temperatures, and attaining resultssomewhat more desirable than those attainable in accordance with theprior art practices.

It is also contemplated in accordance with the present invention, that apredetermined temperature may be used, when heat treating a metallicarticle including two or more metals, which predetermined temperatureWill' be below the melting point of the highest melting point of one ormore lower melting metals present. Using this I. I 8 3 5 3 phasezof'gthefinvention, some one or more of the lower I I 50 P- I I B EQ P if h i fl fid I I I I I I melting rnetals, :rinay; :in? If'aIctQ; becaused to I fuse 'th u i 'n pure hydrogen at 1800 13. throne hour..OtheVPa'rts I I I I serving. to i bind togeth' 'rI ftheI unjfused pa,cleis as '01 redu ed n t sam w y. bu co t n 90% ir n n highglf n i gmsI I I I I f II I j j I 0% copper {by weight); I were; sintered for thesa me f I ;iIn accompanyingdrawingsgthereis illustrated j ija hi Iimejand 'at'th same temperatur nat QspeheIeIcoW cally some of thedesirable results of the present ,inv'e'n :sisting; lot; 95% I hyd o enan 5 I gas y o me; I I I I I ass ss thatfthese results maybe visnalizedmore easily I T he telf sile strength f: the parts sintered in pure.hy-: I than-could be done frornZm ere tabulated Iresnltsg I I f I I I ei I 15,000 ii an he reldngfationwas 1.5%; I I I In the drawings; I I I II I I I I I I I. I I j I 'Tliejcopper ironparts that were 'sintered' inthe atmos- I I I I I I Figure 1 isa plot showing the relation-between.t' eo sile' shar 2 c n a ning 5%: HBr as; aforesaid had: a tensile I Istrength and. 'sintering temperature in articles. pIreIvi- I I streng 391?- anfielongflfioh Of 210%? E F I f f I I I i ou'slypressed05550000: s.hand with inherent Iceman though;the COmQ SitiQ 0 6 tw typ p' r sz t I II I I I I I I I I I respect toiron and copper ditfered; slightly, thisexample; I

1 illustrates that, shite-ring :in. an. atmosphere, i containing 5 i iHi-3r has a beneficial effect; on the tensile {strength of; II

I mixed pe per-h n: powders The differences I in tensile I I strengthwas. much greater than could be attfa iditferences; in composition. I Ii trations of HBr present in the. atmosphere duringisi nter f I I I ing,alegendbelow theplotfindicating the percent HBr usedfoieach cnrve;gand I'I '"I I I I I I I Fig. 2 is: a plot showing the relationship between: II I tensile: strength; and geoncentratiqn; {b olutne), in.

- the gaseous atmosphere during sinterihg, the c I 3 I I I shown for;different temperatures as marked rashes I I thereon and; the materialiused. for; all curves being. iron owder pressed at 50,000 I i.- f I f II I I I I I I f I I :Inithefaccompanying;draw1ngs, a oomparis I with fthe; prior: art which is .that czorrditior represented I by;0%HB1-' I Itwill be noted frornltfhe jse rail-cnrvesfthat ubst-antially I enhancedresults {as to: tensile: strength; :a t. rained when; progressively/greater concentrat f 05 I HBr' are presentin, the I gases from iaboutl,% up to I {Met-a1 parts were prepared by mixing; 97% n I iI'OIXl I I II g ewter; and? 3% of nickel poiwderf :(by: weight). and I I pressingthe mixed ewdersat'saooo p.; 5 S ine gofi I 'hese parts were sinteredfor oneIho'ur in an atmosphere I I I I I hydrogen t 1800"; R, whileothers, having the. amecompos'ition; were Sintered under theisjarnempndi ons or time: and temperature in an atmosphere consist. hy nc 5 BB1"; a v l me- T e;

'intere'd' in pure: hydrogen had tensile strength; I 280p. s. i. aridanelongation 3.1%, W hi le the arts; of. th same composition inter ed inthe a I bout 5%; and that these r'esjults aredifierentfrom those- Iobtainableby prior art practice to; a substantial. and: surI prisingextent. WhiIe Ithe Eata forrriing Ithe; bases the eurv'es shown in; thedrawings was obtained Easing: I I 3 P I I I I I I I I pow ered non Itssnieses, similarresults a e obtainablef ma e a e s BB amn i It a a tensileren I uSing' othermetals or combinations t-hereof; :1 set; forth; I I I9 a d an: fl j i j Ih e I I I I I The? data illustrated {in Figs; :1.and I 2 is set forth; in .i "j i Tabla? I I l i 90% copper'powdc r and.10% tin' powder y weight}, I I I TABLE 'I f II I I I were prepared bymixing these two powders andpress'ing I I I I I1. g e ts-g I .1 I I I themixed powders to a desiredshape at 50,000 p. s. i. I

I I I I 3 3 i I Some of -tjhes'e parts were sinteredforf one hour at. ai I I I I llrbn powdcr pressed 005000 I Percentage HBr in Tensile ITemperature. E longation temperature 0f 1475 .F.',' Wl-1il6 01113118were. sintered line; I I

by f Yemnt der the same conditions .in .an atmosphere consisting of I I95% hydrogen and 5% HBr gas by volume. .These parts 10 240 1.600 M)sintered in pure hydrogen had .a tensile strength of 81640 11000 2.714,040 p. s. 1. and an elongation of 0%, .while those I 1%238 ggg g;sintered in the atmosphere including HBr gas aforesaid 1" 610 1:600 810had a tensile strength of 28,700 p. s. i. and an elonga- 15 610 11600tion of 17.0%. In this mixture particularly, the ad- 10,340 1,800 3.3vantage of sintering in HBr-containing atmosphere are g: 2%? h2g8 Zstrikingly illustrated, especially with regard to improv- 17,680 1,8007.3 ing the percent elongation. 18,080 1,800 8. 0 17,4 30 1,800 0.7Example 4 3:298 888 As an example of the application of the inventionwith 15', 670 2: 000 010 5r gases of.a non-reducing, neutral character,the results of ig ggg 888 2:; slnterlng powdered iron parts in anitrogen atmosphere 191720 2,000 5.3 are set forth below. Samples wereprepared from the same type of powdered iron employed in the testsreported in Figs. land 2 and in Table I above b pressin From 'I able Iabove, it will be noted that the results the iron powder to a desiredshape at 6 obtained In terms of tensile strength and elongation for someof the test Pieces so Prepared were sintered for one the tasts madeusing. 05% B P p are lower hour at 1800 F. in an atmosphere of purenitrogen, while than the results obtained by srntermg 1n pure hydrogen.Others were Sintered under the Same conditions in an On the other hand,in the preferred higher concentrations atmosphere Consisting of 90%nitrogen and 10% of at i 5% positively improved results gas by volume.The test pieces sintered in the atmosare obtained in respect to theprior art wherein no HBr phere of Pure nitrogen had a tensile strengthof 11,130 ,i f h f th p. s. i. and an elongation of 0.9%; while thosesintered e app lcanon 0 t PIOFBSS 0 e mventwn. to in an atmospherecontaining I-lBr had a tensile strength various powdered metalsincluding metals other than iron of 16 600 p s i and an elongation of 80% Thus it may be Illustrated by the following examples will be seenthat as compared with using a neutral atmos- Example I phere such asnitrogen, theaddition of HBr substantially Powdered metal parts weretested consisting of 92.5% enhanced the P y Properties Of a heat treatediron powder and 7.5% copper powder (by weight), propowdered metal part.However, it will be noted by duced by mixing copper and iron powders inthese pro comparison with the data set forth in Table I, that theportions and pressing the mixed powders to shape at 75. increase intensile strength is not as great as when the heat treatment is carriedout in an atmosphere containing hydrogen.

During the tests on the heat treatment of iron articles in an atmosphereof nitrogen and HBr, the presence of FeBrz was observed in the exitgases. It is believed that during the process, the beneficial effects ofthe HBr were partially counteracted by the formation and subsequentvolatilization of FeBrz, which weakened the product physically to someextent. However, this undesired bromidization did not take place to suchan extent as to prevent the HBr from enhancing the tensile strength ofthe part as compared with a similar part sintered in an atmospherecontaining no HBr. This example is further submitted to illustrate thebeneficial effects of the presence of a reducing gas such as hydrogen.

Example This example illustrates the use of the present process inconnection with a pre-alloyed brass powder consisting of 90% copper andzinc by weight. Zinc is a metal which is relatively easy to bromidize ascompared to such metals as iron, nickel, copper, etc. Test samples wereprepared from the pressed alloy powder, described above, by pressing at50,000 p. s. i. Some of these samples were sintered for one hour in anatmosphere of pure hydrogen at temperature of 1620 F., while others weresintered under the same conditions in an atmosphere consisting of 95%hydrogen and 5% HBr gas by volume. The parts sintered in the atmosphereof pure hydrogen had a tensile strength'of 10,150 p. s. i. and anelongation of 3.6%; while those sintered in the HBrcontaining atmospherehad a tensile strength of only 8,680 p. s. i. and an elongation of only2.5%. The decrease in tensile strength and percentage elongation causedby the sintering in a HBr-containing atmosphere is believed to be due tothe fact that the relatively reactive zinc-containing powder, combineswith the HBr gas to form zinc bromide, which volatilizes at thetemperatures employed, leaving the structure of the part substantiallyweakened. This material is not to be considered as within the scope ofthe present invention.

Example 6 TABLE II Iron powder having diiferent amounts of admixed FeBrzwere pressed at 50,000 p. s. i. before heat treatment:

Percentlgolid FeBr in Temperature, F. Tensile Strength,

' s p. s. i.

ixture From the data given in Table II, it will be seen that the effectof adding solid ferrous bromide is to decrease, rather than to increase,the tensile strength of the parts. The process of the present inventiondoes not include sintering powdered metal parts in which solid halidesare admixed with the powdered metal in lieu of otherwise supplyinggaseous HBr in the atmosphere in which the parts are heat treated.

When one sample of Swedish iron powder, compacted at 50,000 p. s. i; wassintered in an atmosphere of pure hydrogen, at 1800 F., the resultingarticle had a tensile strength of about 10,000 p. s. i. A second sampleof the same Swedish iron powder having 0.5% FeBrz thoroughly admixedtherewith was compacted at the same pressure of 50,000 p. s. i. and thensintered at the same temperature of 1800 F., resulting in a test piecehaving a tensile strength of only about 7000 p. s. i. A third sample ofthe same powder, having the same 0.5 admixed FeBrz and compacted at thesame pressure of 50,000 p. s. i., was then sintered at the sametemperature of 1800 F., this time in an atmosphere consisting ofhydrogen and 5% HBr (both by volume). This sample had a tensilestrength, measured by the same test, of about 9800 p. s. i. Thisdemonstrates that while the presence of admixed bromide has an undesiredeifect of lowering the tensile strength of the final article, thepresence in the sintering atmosphere of HBr derived from a source otherthan reaction between admixed bromide and a reducing gas constituent ofthe sintering atmosphere, will result in enhancing the tensile strengthas contrasted with the results obtainable when using a sinteringatmosphere in which HBr is absent. It is reasonably to be concluded,therefore, that where the amount of admixed bromide in the metallic bodybeing sintered is minimized and is not too great, the desirable effectsof the presence of HBr in the sintering atmosphere may not onlycompensate for the undesired results due to admixed bromide, but maygive superior results, notwithstanding a minor diminution of the tensilestrength by small amounts, as traces, of admixed bromide.

While the process of the present invention has been disclosed as appliedto a limited number of the many possible combinations to which it isapplicable, the principles herein set forth are applicable generallywithin the limits stated. It is intended that the appended claims shallbe construed to cover all'reasonable equivalents as will occur to thoseskilled in the art from the foregoing particular disclosure, and thatthe claims be construed validly as broadly as the state of the prior artpermits.

What is claimed is:

l. The process of making metallic parts with a metallic material of atleast one of the relatively difiicultly bromidizable powdered metalsselected from the group which consists of iron, nickel, cobalt, copper,cadmium, lead, tin and molybdenum, and wherein the amount of bromidesintermixed with said metallic material is minimized, said processcomprising the step of heat treating said material in a non-oxidizingatmosphere, establishing and maintaining in said atmosphere aconcentration of at least about 1% of gaseous HBr by volume, bysupplying gaseous HBr to said atmosphere from a source independent ofany intermixed bromine-containing material in said solid material, saidheat, treating being eifected, by raising the temperature of saidmaterial to the point at which at least one metal present is brought tothe point of incipient fusion in said atmosphere.

2. The process in accordance with claim 1, the volume concentration ofgaseous HBr in mosphere is from about 1% to about 15%.

3. The process in accordance with claim 1, the volume concentration ofgaseous HBr in mosphere is about 5% to about 15%.

4. The process in accordance with claim 1, said non-oxidizing atmospherecontains hydrogen.

5. The process in accordance with claim 1, wherein said non-oxidizingatmosphere consists essentially of a mixture of gaseous HBr andhydrogen.

6. The process in accordance with claim 1, wherein said non-oxidizingatmosphere consists essentially of a mixture of gaseous HBr andnitrogen.

7. The process in accordance with claim 1, wherein said heat treating iscarried on at substantially the same wherein said atwherein saidatwherein temperature at which some one 'metal present-in said metallicmaterial will sinter in the same atmosphere without HBr-present therein,so as toproduce a part having enhanced physical properties in respect tothe corresponding physical properties of such a part sintered in thesame atmosphere but without HBr therein.

8. The process in accordance with claim 1, wherein said heat treating iscarried on at a temperature substantially below that temperature atwhich some one metal present in said metallic material would sinter bybeing brought to the point of incipient fusion in the same atmosphere inthe absence of HBr therein, so as to produce a part having substantiallyas desirable physical properties as the part would have if sintered bybeing brought to the point oflincipient fusion in the same atmosphere inthe absence of HBr therein at said temperature at which some metalpresent would sinter as aforesaid in the absence of HBr.

9. The process in accordance with claim 1, wherein said heat treating iscarried on at a temperature somewhat lower than that at which some onemetal present in said metallic material would sinter by being brought tothe point of incipient fusion in the same atmosphere in the absence ofHBr therein, so as to produce a part having somewhat enhanced physicalproperties in respect to the properties which would be present in asimilar part sintered as aforesaid in the same atmosphere in the absenceof HBr at said temperature at which this metallic material would sinteras aforesaid in such atmosphere in which HBr was absent;

10. The process in accordance with claim 1, wherein said metallicmaterial is powdered iron, and wherein said atmosphere contains fromabout to gaseous HBr by volume.

11. The process in accordance with claim 1, wherein said metallicmaterial is powdered iron.

12. The process in accordance with claim 1, wherein said metallicmaterial consists of iron and nickel, and wherein said atmospherecontains about 5% gaseous HBr by volume, the temperature of the heattreatment being at least that at which nickel powder is brought to thepoint of incipient fusion. 1

13. The process in accordance with claim 1, wherein said metallicmaterial consists of copper and tin, and wherein said atmospherecontains about 5% gaseous HBr by volume, the temperature of the heattreatment being at least that at which tin powder is brought to thepoint of incipient fusion.

14. The process in accordance with claim 1, wherein said metallicmaterial consists of copper and iron, and wherein said atmospherecontains about 5% gaseous HBr by volume, the temperature of the heattreatment being at least that at which copper powder is brought to thepoint of incipient fusion.

15. The process of making metallic parts starting with a metallicmaterial containing at least two of the rela- 12tivelydifiicultly'bromidizable powdered metals selected from the groupconsisting of iron, nickel, cobalt, copper, cadmium, :lead,tin andmolybdenum, and whereinthe amount QfbromidesintermiXed with saidmetallic material is minimized, said proccsscomprisingthe step of heattreating said material in a non-oxidizing atmosphere, establishingandmaintaining in said atmosphere a con centration of at least about 1%of gaseous HBr by volume, by supplying gaseous HBr to said atmospherefrom a source independent of any intermixed brominecontaining materialin said solidmaterial, said heat treating being eifected by raising thetemperature of said material to a point at least ashigh as that at whichat least one metal present is'br'ought to the point of incipient fusionin said atmosphere and below the temperatnre at which the highestmelting metal present will melt.

16. The process'of making metallic parts by powdered metallurgypractices, starting-with a metallic material of at least one of therelatively difficultly bromidizable powdered metals selected from thegroup which consists of iron, nickel, cobalt, cadmium, lead, copper, tinand molybdenum, and wherein the amount of bromides intermixed withsaidmetallic material is minimized, said process comprising the steps ofcompacting said metallic material at a predetermined pressure to adesired form for a part to be made, and heat treating said material in anon-oxidizing atmosphere, establishing and maintaining in saidatmosphere a concentration of at least about 1% of gaseous HBrby volume,by supplying gaseous HBr to said atmosphere from a source independent ofany intermixed bromine-containingmaterial in said solid material, saidheat treating being effected by raising the temperature of said materialto a point at which at least one metal present is brought to the pointof incipient fusion in said atmosphere.

17. As a new product, a metal article consisting essentially of sinteredpowdered metal selected from the group which consists of the metals:iron, nickel, cobalt, copper, cadmium, lead, tin, and molybdenum andmixtures and alloys consisting essentially of saidmetals, and

wherein the amount of bromides intermixed with said metallic material isminimized, said article being prepared by the process of claim 1.

References Citedin the file of this patent UNITED STATES PATENTS

1. THE PROCESS OF MAKING METALLIC PARTS WITH A METALLIC MATERIAL OF ATLEAST ONE OF THE RELATIVELY DIFFICULTLY BROMIDIZABLE POWDERED METALSSELECTED FROM THE GROUP WHICH CONSISTS OF IRON, NICKEL, COBALT, COPPER,CADMIUM, LEAD, TIN AND MOLYDENUM, AND WHEREIN THE AMOUNT OF BROMIDESINTERMIXED WITH SAID METALLIC MATERIALS IS MINIMIZED SAID PROCESSCOMPRISING THE STEP OF HEAT TREATING SAID MATERIAL IN A NON-OXIDIZINGATMOSPHERE, ESTABLISHING AND MAINTAINING IN SAID ATMOSPHERE ACONCENTRATION OF AT LEAST ABOUT 1% OF GASEOUS HBR BY VOLUME, BYSUPPLYING GASEOUS HBR TO SAID ATMOSPHERE FROM A SOURCE INDEPENDENT OFANY INTERMIXED BROMINE-CONTAINING MATERIAL IN SAID SOLID MATERIAL, SAIDHEAT TREATING BEING EFECTED, BY RAISING THE TEMPERATURE OF SAID MATERIALTO THE POINT AT WHICH AT LEAST ONE METAL PRESENT IS BROUGHT TO THE POINTOF INCIPIENT FUSION IN SAID ATMOSPHERE.
 17. AS A NEW PRODUCT, A METALARTICLE CONSISTING ESSENTIALLY OF SINTERED POWDER METAL SELECTED FROMTHE GROUP WHICH CONSISTS OF THE METALS: IRON, NICKEL, COBALT, COPPER,CADMIUM, LEAD, TIN AND MOLYBDENUM AND MIXTURES AND ASLLOWY CONSISTINGESSENTIALLY OF SAID METALS, AND WHEREIN THE AMOUNT OF BROMIDESINTERMIXED WITH SAID METALLIC MATERIAL IS MINIMIZED, SAID ARTICLE BEINGPREPARED BY THE PROCESS OF CLAIM 1.